IP multimedia subsystem (IMS) networks allow IMS-compatible devices to establish voice calls and to receive call originating and call terminating services using IMS network elements. In an IMS network, an IMS-compatible subscriber device, such as an IMS-compatible handset, is homed to a serving call session control function (S-CSCF). When an IMS-compatible device connects to a network anywhere, the IMS-compatible device first obtains an IP address. The IP address may be obtained by static assignment or by a dynamic protocol, such as DHCP. The IMS device then registers with the home S-CSCF. Registration involves communicating the IMS device or subscriber identity and the corresponding IP address to the S-CSCF. For example, IMS devices may be identified by SIP URIs. An example of an IMS device identity that may be associated with an IMS subscriber's SIP phone is Dan@Tekelec.com. The SIP phone may obtain an IP address of 196.10.10.1 when the phone connects to the network. Registration of the SIP phone involves communicating the association between 196.10.10.1 and Dan@Tekelec.com to the subscriber's S-CSCF. Registration of IMS devices can be accomplished through SIP messaging between the devices and their respective S-CSCFs.
Once an IMS device is registered with its S-CSCF, the device can originate and terminate calls and receive call originating and call terminating services using IMS network elements. For example, when the IMS device originates a call, the S-CSCF is notified of the call origination and queries a database, referred to as a home subscriber server (HSS) database, to determining call originating services to be applied to the call. Examples of call originating services include prepaid calling services and number portability services. The S-CSCF may then obtain routing information and invite the terminating device to the join the call. If the IMS device is at the terminating leg of the call, the S-CSCF receives an invitation for the device to join the call, determines the terminating services to apply to the call, and signals with the originating S-CSCF to establish the call.
It may be desirable to establish calls and to provide services using IMS nodes to non-IMS devices, such as 2G mobile phones and PSTN phones or black phones. 2G mobile phones and black phones are incapable of receiving calls or services using IMS network elements because such devices are not identifiable to the IMS network. For example, black phones and 2G mobile phones are incapable of registering with the IMS network because they do not have registration signaling capabilities. As a result, such devices can receive calls and services only by relying on PSTN network elements. Consequently, such devices may be limited in the types of service that they can receive and may be charged more for such services than the corresponding services available via the IMS network.
Accordingly, in light of these difficulties, there exists a need for methods, systems, and computer program products for providing Internet protocol multimedia subsystem (IMS) registration services for non-IMS devices.